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UNIT-I
1.1 INTRODUCTION:
With increase in population the need for electricity also increases therefore it is necessary to rise
number of electrical engineers. The electrical engineering mainly deals with generation ,
transmission and distribution of electricity.
Electrical circuits is the basic and fundamental subject which lays path
to understand subjects related to generation , transmission and distribution of electricity.
In the first unit we shall deal with what is electrical circuit and formation
of electrical circuit. Knowing or unknowing we come across electron in our life daily, studying
the properties of these electrons leads to the terms voltage, current and power. Hence the basic
definitions of voltage , current , power and energy are studied here.
1.2 CIRCUIT:
The electrical circuit consists of mainly three parts , they are -- source, connecting wire and load
or sink.
Source :
An source may be battery which forces electrons into the circuit.
Connecting wire : This is part which provides path for electrons to flow.
Load : The load may be bulb etc. when electrons flow through it an reaches the
Source it glows .
If the electrons are provided closed path to flow, leads to current is called as electrical circuit.
1.3 BASIC DEFINITIONS:
Voltage(V) : The potential difference between force applied to two oppositely charged particels
to bring them as near as possible is called as potential difference .( in electrical terminology it s
voltage).
V = W / Q (v)
υ = dw / dq (v)
v-
volts , units of voltage.
Unit volt is defined as 1C of charge developed when
1 J of energy is applied.
Current(I) : The flow of electrons develops the current.
I = Q/ t (A)
i = dq / dt (A)
A = Ampere, units of current.
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Unit ampere of cuurent is constituted when 1C of charge is flowing in
1S.
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Power(P): It is defined as product of volateg and power in electrical circuits or
Rate of change of energy.
P = dw/dt = dw/ dq . dq/dt = υ .i (W)
W = watts, units of power.
Unit watt is the 1J of energy is dissipated in 1S.
Enegy : It is the capacity to do work or it is defined as power consumed over
Given interval of time.(w)
W = ʃ P dt.(J)
J = Joules, units of energy
1J = 1 watt-sec.
1.3 BASIC PARAMETERS:
Any electrical mainly consists of three important elements , they are resistor, inductor and
capacitor. Let us deal these parameters in detailo.
1.3.1 Resistor: resistor is the element which restricts flow of electrons and this
Property of opposing electrons is called as resistance.
OHM’s Law : ohm’s law states that current flowing through circuit is
Directly proportional to potential difference applied.
( at constant temperature)
I α V, at constant T.
I.R = V.
R = V / I, hence resistance can be calculated as ratio of
Volatge to current in any element or circuit.
= OHMS ῼ, units of resistance.
R=
1.3.2 Inductor: An length of wire twisted forms the basic inductor.(L). when
Alternating curent is allowed through such a element it induces
Voltage in it.
e, ɸ
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